1. Field of the Invention
The present invention relates to a semiconductor device and, more particularly, to a connection structure of an external connection electrode terminal portion of a semiconductor element.
2. Description of the Related Art
In order to achieve miniaturization, high-performance and low-cost for electronic equipments, there is a demand for miniaturization, higher-performance and low-cost in semiconductor devices to be mounted on the electronic equipments. As one of external connection electrode terminal structures of such a semiconductor device, there is a structured using a solder bump. Thus, with such a demand for miniaturization of the semiconductor devices, a solder bump as an external connection electrode terminal has also been miniaturized and reduced in a diameter.
On the other hand, an amount of electric current flowing in such a semiconductor device tends to be increased so as to achieve a higher-speed operation of the semiconductor device. Thus, a current density of a current flowing through one solder bump is increased, which causes an electro-migration in a solder material constituting the solder bump and/or a foundation metal layer of the solder bump. Accordingly, there is a high possibility of a void (cavity) being generated in the solder bump. An existence of such a void may decrease a cross-sectional area of a current path in the solder bump, which results in an increase in an electric resistance. Thus, the existence of the void gives bad influences to an operation speed of the semiconductor device and also results in a decrease in reliability of the semiconductor device.
As a solder material for the solder bump, a so-called lead-free solder material has become widely used. Such a lead-free solder material is considered to have a lower resistance to electro-migration than a conventional lead-containing solder.
FIG. 1 shows an example of a solder bump portion of a semiconductor device having external connection electrode terminals formed by solder bumps.
In FIG. 1, a terminal pad portion 2 is formed in an aluminum (Al) wiring layer formed on one of main surfaces of a semiconductor substrate 1. A solder bump 7 formed of a tin (Sn)-silver (Ag) solder is provided on the terminal pad portion 2 via a foundation metal layer 6 constituted by a titanium (Ti) layer 3, a copper (Cu) layer 4 and a nickel (Ni) layer 5. An area where the terminal pad portion 2 and the foundation metal layer 6 are in contact with each other is defined by a surface protective film containing a passivation layer 8 formed of silicon nitride and a polyimide layer 9 covering the passivation layer 8.
In the above-mentioned external connection electrode terminal structure, an electric current may concentrated in a portion from which the wiring layer 21 extends, that is, at an end portion of the foundation metal layer 6 in a connection area where the foundation metal layer is connected to the wiring layer 21 under the foundation metal layer 6 of the external connection electrode terminal, as illustrated in FIG. 2. That is, electrons (e−) flowing into the solder bump 7 are concentrated at the end portion of the foundation metal layer 6, and electro-migration may occur in the solder bump 7 and/or the foundation metal layer 6. As a result, a void (cavity) 22 may be formed inside the solder bump 7.
It should be noted that active elements and/or passive elements are formed by a normal semiconductor process inside the semiconductor substrate 1 shown in FIG. 1. Additionally, a so-called multi-layer wiring structure is provided on the main surface of the semiconductor substrate 1, and the active elements and/or the passive elements are electrically connected to each other. The terminal pad portion 2 for external connection is selectively provided in the middle of the wiring layer or an end of the wiring layer.
The following Patent Documents disclose the above-mentioned bump structure.
Patent Document 1: Japanese Laid-Open Patent Application No. 2000-195866
Patent Document 2: Japanese Laid-Open Patent Application No. 2002-16065
As mentioned above, electro-migration may occur in the external connection electrode terminal and/or the foundation metal layer under the external connection electrode terminal due to local concentration of an electric current flowing between the external connection electrode terminal and the wiring layer in the connection portion between the wiring layer and the external connection electrode terminal provided on one of the main surfaces of the semiconductor board. As a result, a void (cavity) is generated inside the bump constituting the external connection electrode terminal. This may invite an increase in a resistance of the external connection electrode terminal portion, and further a decrease in reliability of the semiconductor device.
Therefore, in the connection portion between the wiring layer and the external connection electrode terminal, it is required to acquire a connection structure, which does not have a possibility of generating a local concentration of an electric current.